Why people let a dictator rule themselves?

Even his power also lies in people then why people don't understand this and let anybody rule themselves.Like in case of Gaddafi , or even ongoing situation in north korea..how can a single person or a small group of people rule large mass so easily ?

Apr 7 2014:
The thing is that initially a dictator isn't necessarily perceived as a dictator but as somebody who offers solutions to existing problems.
Hitler is a good example for that. He promised to improve the living standard of Germans after the great depression and actually did when he started to build up supplies and infrastructure for WWII.
At the same time he created a common enemy (the Jews) on which he blamed all the problems Germans experienced at that time.
Once people figured out (some never did) what's actually going on, Hitler was far too powerful to easily get rid of him. It took a World War to finally remove him.
Other countries such as N-Korea hold out much longer because there is no real international incentive to do something about it (N-Korea has no particular strategic value to nations that could do something about the situation)

Apr 3 2014:
In many instances, e.g the middle east, Russia, the people have never had anything but either monarchism or dictators (plus religious leadership). This means they expect and even need to see this in their leaders. Democracy is somewhat alien to them. This long history makes people think that a strong leader needs to act like a dictator for example. Anyone trying something quite different then fails to gain respect.